The technique currently used to wrap monobloc articles of a predominantly prismatic shape with heat-shrinkable material, or more frequently to wrap groups of individual articles formed, for example, by containers of products, in particular, food products and the like, and having this monolithic prismatic shape, hereafter called articles for simplicity, involves the use of discontinuously or continuously operating automatic machines constructed to wind the heat-shrinkable material about the individual articles to be wrapped in a number of ways.
Using this wrapping technique it is conventional to wrap the article to be wrapped with the heat-shrinkable strip material in the direction of its movement such that this material projects from two opposite faces of the article and then to pass this assembly through a tunnel furnace to cause the material to adhere by heat shrinkage to the wrapped faces and to the two opposite faces of the article by folding the corresponding material over these latter faces.
Some of these known machines for wrapping such individual articles caused to advance intermittently or continuously in a continuous sequence and uniformly spaced from one another use two strips of the heat-shrinkable material which, at a sealing station, are brought rhythmically upwards and downwards between two successive articles where they are transversely joined by soldering and then cut so as progressively to determine the closure or sealing of the wrapping or winding of a previous article and the joining of the same strips for winding of the following article. The articles wrapped in this way are then passed through a tunnel furnace to cause the material to adhere to the wrapped faces by heat shrinkage and to the opposite two faces of the article by folding of the corresponding material over these latter two faces (see for example, the U.S. Pat. Nos. 3,869,844 and 3,927,507).
Other known machines designed to wrap such articles caused to advance continuously with a uniform spacing make use of a single strip of the heat-shrinkable material.
One of these known machines supplies the strip parallel to the direction of movement of the articles which are uniformly spaced in a longitudinal direction. The strip or web is folded progressively as it advances into a tubular shape with its respective longitudinal edges superimposed about the articles being supplied and these superimposed edges are joined by heat sealing. The articles wrapped or enclosed in the tube are then caused to pass, continuing their continuous movement, firstly through an initial station or initial tunnel furnace for initial heat shrinkage of the material about the articles and then, on discharge from this initial station, through a second station designed to cut the tube between two successive articles so as to provide projecting material about the whole of the front and rear faces of two successive articles. The articles are then passed and finally through a third station or a second tunnel furnace to complete the adhesion by heat shrinkage of the material to the wrapped faces and the front and rear faces of the article by folding the corresponding material over these latter two faces (see British Patent Specification No. 1 382 842).
In another of these known machines using a single strip or web to wrap articles supplied continuously with a uniform spacing the strip is supplied downwardly so as to extend it over the articles and projects from two opposite lateral faces, and to bring it, unwinding it downwardly from a corresponding spool, into a folded loop shape between successive articles and to push it in the direction of supply of the articles below the preceding article where the loop section is cut providing two ends or flaps of wrapping material, i.e. a rear flap for the preceding article and a front flap for the immediately following article.
During the continuous movement of the articles, the flaps for each article are superimposed on one another on the lower face or base of the article and the articles wrapped in this way are, during their continuous movement, then brought successively inside a tunnel furnace so as to cause the wrapping material to adhere by heat shrinkage, as is conventional, to the wrapped faces and to the two opposite faces of the article by folding of the corresponding material over these latter two faces (see British Patent Specification No. 1 355 571).
The prior art relating to packaging also discloses the method of bringing sheets or sections of wrapping material cut progressively from a strip wound on a supply spool across the path of the continuously moving articles to be wrapped so as to fold them into the shape of a horizontal U over the front face and the parallel upper and lower faces adjacent thereto of the articles with the end portions of the prongs of the U extending beyond the rear face and then to fold these end portions over the rear face and to join or seal them in a partially superimposed manner. The means provided to embody this packaging method are normally formed by at least two pairs of opposite closed circuit belt means designed to grip the longitudinal edges of these sheets in order to bring them across the path of movement of the articles to be wrapped (see British Pat. No. 1 037 261 and U.S. Pat. No. 2,424,406). To such closed circuit means disposed at the longitudinal edges and designed to entrain them by suction (see British Pat. No. 958 377 and U.S. Pat. No. 3,871,257).
Machines which use this latter method of folding the wrapping material into a U shape with the folding and final joining of the edges of the sheets by sealing at the rear faces of the articles to be wrapped require complicated devices both for the final folding operation and for the sealing operation, as a result of which, in the case of machines for wrapping articles with heat-shrinkable material which are already provided with a tunnel furnace to cause the heat-shrinkable, and therefore heat-sealable, material to adhere to the articles by heat-shrinkage, it is preferred, although not always possible, to use the method described above which involves initial folding of the heat-shrinkable material about the front, upper and rear faces of the article in the shape of an upturned U and then folding and partial superimposition of the end portions of this upturned U on the lower face of the article.
Attempts to eliminate these complicated folding and sealing devices for portions of flaps on the rear face of the products using the heat source of the tunnel furnace to join and seal the superimposed portions of the flaps of the U of wrapping material on the lower face of the articles at the same time as the operation in this furnace to cause the heat-shrinkable wrapping material to adhere to the product by heat shrinkage so as to provide greater flexibility, i.e. a higher production speed per unit of time, and a more economic cost for these machines for wrapping with heat-shrinkable material, have not in practice enabled the achievement of these objectives as a result of the complexity of the apparatus used for folding and superimposition of the end portions of the material in the shape of an upturned U on the lower faces of these articles (see, for example, the above-mentioned British Patent Specification No. 1 355 571).
Applicants has also used this method in U.S. Pat. No. 4,574,565 proposing and subsequently which discloses a machine for wrapping articles supplied with a uniform spacing by means of a continuously moving conveyor with sheets cut progressively from a strip of heat-shrinkable material projecting from two lateral faces of these articles and brought in succession by suction take-up means along their respective longitudinal edges across the path of movement between individual successive articles so as to be folded over the front, upper and lower faces of a corresponding article in the shape of an upturned U extending beyond the rear face so as to be folded over this rear face and superimposed on the end portion folded over the lower face, this conveyor being formed by two adjacent conveyor belt sections and the said take-up means supported at the zone between the two adjacent belt sections and in which the adjacent zones of the two belts are wound on at least a corresponding pair of return rollers supported by a carriage which may be moved in an alternating manner parallel to the conveyor direction and the take-up means being movable in a vertical alternating manner parallel to the movement of the carriage.